The present invention relates to an optical information reading device which optically reads characters, signs or the like.
Optical information reading devices heretofore in use, especially hand scanners which manually scan characters and the like and optically read them, have a construction as shown for example in FIG. 1. The device recognizes the information of characters and the like by holding the scanner 1 by hand (not shown in the figure) and moving it in horizontal directions over the sheet 2 on which the information is written. The sheet 2 is illuminated by means of the light sources 3a, 3b and the information pattern is imaged via the lens system 4 on the sensor 5 made of photoelectric conversion elements arrayed in one dimension for example or in two dimensions. The output signal of the sensor 5 is processed by means of the pattern identification circuit 6. A power source 7 is used to drive these elements.
In the case of a hand scanner constructed as mentioned above which has heretofore been in use, incandescent electric lamps such as tungsten lamps or the like have usually been used for the light sources 3a, 3b. However, incandescent electric lamps such as tungsten lamps or the like have been found to be a cause of lowered efficiency of the hand scanner because they have numerous shortcomings. Generally, they consume a large amount of electric power and generate large amounts of heat. Also, they have a comparatively short life, and their center of spectral intensity is located in the infrared range where the sensitivity of Si photodiodes generally used as photoelectric conversion elements is reduced so that the matching of these two elements is poor.
On the other hand, for improvement in the operability of a hand scanner, it is necessary to make the area of the scanning opening 1a of the scanner 1 small. However, since incandescent electric lamps themselves are large in size, the number of such lamps to be used is limited. Usually, two tungsten lamps have been positioned facing each other with a lens system 4 inbetween. As a result of this configuration, they become the so-called point light source so that there is a possibility that partial halation occurs depending on the shape of the sheet 2 and this may make it impossible to carry out the reading.
Furthermore, in case where the scanner 1 gets tilted to the left, right, forward or rearward with respect to the sheet 2 or floats up from it, the illumination over the sheet 2 becomes uneven or insufficient. An accurate image of the information pattern may not be formed on the sensor 5 and the reading becomes inaccurate. With the construction of the illumination devices heretofore in use, it has been impossible to prevent this completely.